Background. Serum concentrations of soluble interleukin‐2 receptor (IL‐2R) were found to be high in patients with autoimmune diseases, lung cancer, malignant lymphoma, tuberculosis, and other diseases. Serum‐soluble IL‐2R was evaluated as a tumor maker in patients with gastric cancer. Methods. Preoperative concentrations of serurn‐soluble IL‐2R were examined in 40 patients with gastric cancer. The authors investigated the correlations of serumsoluble IL‐2R concentrations with various characteristics of this cancer (disease stage, gross appearance, depth of the tumor, lymph node metastasis, liver metastasis, peritoneal metastasis, histopathologic grade, serum carcinoembryonic antigen (CEA), alpha‐fetoprotein (α‐FTP), carbohydrate antigen 19‐9 (CA19‐9), and immunosuppressive acidic protein (IAP). Serum soluble IL‐2R concentrations were measured with an enzyme‐linked immunosorbent assay. Results. Levels of serum‐soluble IL‐2R in patients with gastric cancer were significantly higher than those of normal control subjects. Serum concentrations of IL‐2R in patients with lymph node metastasis were also significantly higher than those of patients without lymph node metastasis. There were no significant differences in histopathologic findings (grade, lymphatic invasion, venous invasion). Moreover, serum concentrations of soluble IL‐2R in patients who were IAP positive were significantly higher than those who were IAP negative. Conclusions. Preoperative serum‐soluble IL‐2R concentrations in patients with gastric cancer reflect the occurrence of regional lymph node metastases. Preoperative evaluation of serum soluble IL‐2R concentrations may be a valuable parameter of indicating the probability of lymph node metastasis preoperatively.